Cryogenic separation method for cold box one kind of item pdh

Cryogenic separation method for cold box one kind of PDH project, comprising four plate-fin heat exchanger, six gas-liquid separator, a flash tank, two sets of expansion unit and a cryogenic pump, wherein the first fed through the first plate-fin heat exchanger and the second plate-fin heat exchanger cooling the second vapor-liquid separator backward; second gas-liquid separator after the separated gas into a first end of the expander expands the first expandable three liquid separator is connected; a third gas-liquid separator gas separated in two shares, a fourth gas-liquid separator separates the gas into the third plate fin heat exchanger to another unit by heat exchange dry gas product , a sixth gas-liquid separator separating gas and recycle gas are into the second plate fin heat exchanger; it has a simple process, high product recovery, energy saving, easy to operate, economical and excellent performance characteristics and the like.